Cellular and public-switched telephone networks are well known. Such networks generally include a pool of communication resources or channels that are individually allocated to permit network subscribers to communicate on a one-to-one basis. That is, one subscriber initiates a call to a single other subscriber. Upon allocation of a communication channel for each subscriber by the network infrastructure, the two subscribers communicate over the allocated communication channels. Upon termination of the communication (e.g., by hanging up the telephone or depressing the "END" key on a cellular telephone), the infrastructure de-allocates the communication channels and returns them to the pool for other users.
Although telephone networks adequately permit one-to-one communications, they do not quite so adequately permit group communications. One way telephone networks permit group calling is through three-way calling. In three-way calling, one subscriber must make two phone calls, one to each of the other parties to the three-way call, and must enter a key sequence into his or her own telephone that instructs the telephone to operate as a three-way conference bridge. Consequently, to effectuate a three-way call, a user must engage in activity above and beyond placing a single phone call. Moreover, three-way calling only permits three subscribers to communicate at any one time.
Conference calling is another known way in which telephone networks facilitate group calling. Conference calling requires all participants of the group call to place a telephone call to a conference bridge provider. The conference bridge provider then patches all the individual calls together to effectuate the group call. Although this approach permits group calls that include more than three participants, it requires intervention by the conference bridge provider and requires each participant to place a telephone call.
Dispatch radio communication systems are also known. Such systems provide dispatch or group calls automatically upon the initiation of a dispatch call by one the system subscribers. In addition, many such systems provide one-to-one telephone interconnect capability by including hardware and software that couples a dispatch system resource to a resource of the public-switched telephone network. Although such systems provide both one-to-one and group calls, such systems are independent and often privately owned, thereby limiting the public's accessibility to such systems. Also, since such systems are independent, they require a substantial capital investment in hardware and software to provide both one-to-one and group services. Moreover, such systems permit only one-half duplex telephone interconnect. Thus, in these systems, a telephone network subscriber must be cognizant of the fact that his or her transmission will not be received by the dispatch service subscriber if the dispatch service subscriber is also transmitting at the same time. If the telephone network subscriber is not so cognizant, information transmitted by the telephone network subscriber may not be received by the dispatch service subscriber or, at best, may have to be repeated and retransmitted.
Therefore, a need exists for an apparatus and method for providing dispatch or group call service to an existing public telephone network that permit a full duplex group call to be commenced effortlessly by the user of a subscriber and that do not require modification of the existing telephone network.